The show, in which he elaborates on the fairies, pixies and other mysterious characters in his books by comically connecting them with his own wider family in Ireland, was billed for teenagers. But all he could see were baby buggies in the aisles and a group of wide-eyed toddlers in the front row.
"I thought: 'They're not going to understand a word'," he cringes. "They were bored to tears, they just yawned and the mums were taking calls on their mobiles. I did an hour-and-a-half's show in 25 minutes."
Colfer (45) who lives in a beautiful farmhouse on a four-acre plot in Wexford, says that at least when the comedy doesn't work he can go back to calling himself a writer.
The genial, witty author explains that the stand-up act was borne out of his readings, which just became longer and funnier, until his publicist suggested he did a show. It became so successful that it ended up in the West End and did pretty well in the US too, apart from the Texas gig.
"It was an excuse for me to wax nostalgic about family situations in ways which everybody could understand and identify with. But it's very nerve-racking when you're setting up your stall as 'funnyman' because some people don't laugh."
He has his fingers in other pies, though. He has written a musical, The Lords Of Love, which recently opened at the Wexford Opera House, and is writing his first adult fiction book, a crime novel entitled Plugged, which will be published next spring.
But it is the Artemis Fowl series for which he is best known, and the former primary school teacher still cannot believe its phenomenal success, having sold a staggering 20 million copies worldwide.
His seventh novel in the series, Artemis Fowl And The Atlantis Complex, sees the criminal mastermind dabbling in fairy magic which has messed with his mind. It features Colfer's trademark combination of high-tech gadgetry, high-octane drama and hilarious one-liners.
Colfer's work has been published in 44 countries and he's ranked alongside Philip Pullman, Jacqueline Wilson and Anthony Horowitz as one of the most popular and bestselling children's authors, yet people overseas still can't pronounce his name.
"It's like a different life that I have once every 18 months when I have a book out and I'm that Eoin Colfer talking about Artemis Fowl -- and the rest of the time I'm just at home just being a husband and dad, and being grumpy in the shed.
"People know the names of the books, but they never recognise my name, possibly because no-one can pronounce it."
Artemis Fowl was recently voted readers' all-time favourite Puffin book in an online poll to mark the 70th anniversary of the children's publisher, beating Roald Dahl's Charlie And The Chocolate Factory and Stig Of The Dump by Clive King.
"There must be a mistake somewhere," he half-jokes. "I don't think for a second that my work's better than Stig Of The Dump or Charlie And The Chocolate Factory, but to be in that company is amazing."
There's been talk of a movie ever since the first Artemis Fowl book was published in 2001 -- Colfer secured the largest-ever advance for a children's novel by an unknown author and film rights were sold before the book had even been published. Yet a movie has still not been made.
"It's been 'possibly maybe' for about 10 years now. I did get very annoyed about it and spent a lot of time thinking about it, all to no avail. Now, I don't get too emotionally involved in it."
He says there's one more Artemis book to come, and that will be it. "I'll never kill him off, but I think he'll become a moral person and will have to make a choice of some kind which will test his conscience."
The son of teachers, Colfer had an idyllic childhood growing up in Wexford with his four brothers and it was a natural move to to go into teaching. After 15 years of primary teaching, he went to Saudi Arabia, Italy and Tunisia with his wife Jackie, teaching in international schools, while saving up for a deposit on a house. While on his travels, he began writing.
Artemis was an instant sensation and allowed Colfer to concentrate on writing full-time .
"Its success allowed me to believe that I was a writer and not just dabbling at it in my spare time. I remember being really worried because at the time everybody was looking for the next Harry Potter."
While he's never met JK Rowling, he is eternally grateful to her. "I think she's helped a lot of us in that kids' books are seen as bankable now, so we are given a lot of time by the publishers and it's easier to get reviewed in the papers. We owe her a debt."
Away from the limelight Colfer lives a simple life in Wexford with his wife and two sons, Sean and Finn and has never yearned to become a celebrity.
"Nobody's going to come to Wexford to pursue a story about a leprechaun writer," he smiles.